Standard firearms cartridge cases have historically been modified to create new or improved cartridges. To avoid the tooling costs associated with manufacturing a new case, individual hobbyists and moderate-scale manufacturers will start with a widely available “parent” case, and form it to the desired dimensions. While this has been effective in many instances, there are narrow limitations on the amount of modification that a case can undergo. Therefore, the new case's dimensions are largely dependent on the parent case from which it is formed.
One cartridge formed in this manner is the 17 Aguila, produced by Industrias Tecnos, S.A. de C.V., of Mexico. The 17 Aguila is based on a conventional 22 Long Rifle (LR) case, which serves as the parent. Production of the 22 LR is believed to be in greater volume than any other cartridge or case, and is produced at a very low cost per unit, due to the high volume of manufacturing. This makes it desirable as a parent cartridge, as it affords the manufacturer of a new cartridge adequate margin for the cost of forming it into a new cartridge specification.
The 17 Aguila is a bottle-necked or shouldered version of the 22 LR, with the open end portion of the case necked down to form a reduced-diameter case mouth sized to receive a .17 caliber bullet. This is intended to provide a higher velocity than the 22 LR due to the lower bullet weight, with a higher sectional density providing a higher ballistic coefficient yielding a flatter trajectory. While somewhat effective, necking down the case reduces its volume, which limits the quantity of gun powder propellant that may be used. This limits the projectile velocity for a given projectile mass, which limits the effective range of the cartridge.
In commercial production of modified cases, modifications are limited to diameter reductions by necking down the portion at the case mouth, and length reductions by trimming. In low volumes, individual hobbyists may “fire form” centerfire cases (i.e. those having replaceable primers) by shooting a live parent cartridge in a firearm with a chamber sized for the desired new slightly larger case dimensions. This expands the case outward to provide a larger case volume, by reducing the taper of the case wall, or by moving forward and/or sharpening the angle of the shoulder of a bottlenecked cartridge. However, even if this were practical and economical for manufacturing volumes, it would be incompatible with rimfire cases, which are not reusable due to the lack of a replaceable primer, which is spent upon first use.
Consequently, because of the inherent limitations on case forming, the volume of the ubiquitous 22 LR case can not readily be increased in diameter or length to provide increased volume. The performance of .17 caliber cartridges based on 22 LR cases is therefore limited, and manufacturers have avoided utilizing alternative rimfire cases having larger case volumes due to their much lower production volume and therefore prohibitively high cost.
The present invention overcomes the limitations of the prior art by providing a firearm cartridge with a rimmed metal case having a body portion having a rim and a cylindrical wall portion adjacent to the rim. The body portion has dimensions corresponding to a 22 Long Rifle specification. The case has a tapered shoulder portion contiguous with the first portion, and a neck portion contiguous with the shoulder portion and a defining a mouth. The mouth tightly receives a bullet having a diameter less than .22 caliber, and the case has a length significantly greater than the 0.66 inch length of a conventional 22 LR. The case may be formed with a neck that is relatively short compared to the body portion and overall length, to provide improved cartridge performance.